The last 10 years have witnessed great advances in the understanding of the metabolism of alcohol and of the genetics and structure of the enzymes that catalyze the steps of this metabolic pathway. Specifically, the amino acid, cDNA and genomic sequences of the low Km, mitochondrial aldehyde dehydrogenase (ALDH2), the main enzyme of acetaldehyde metabolism, have been elucidated. The activity of this enzyme is deficient in about half of Asians. Furthermore, the deficient phenotype is determined by a dominantly acting allele (ALDH2*2). Individuals with one or two ALDH2*2 alleles are unable to metabolize acetaldehyde normally when they drink and experience a syndrome of flushing and headache which is generally considered aversive. It has been found that deficiency in ALDH2 activity reduces alcohol consumption as well as the risk of alcoholism. The administration of drugs that inhibit ALDH2 such as cyanamide or disulfiram also cause an aversive flushing reaction, but the clinical efficacy of treatment with these drugs is limited by their lack of specificity and short duration of action. With the maturing of gene therapy technologies, it is now possible to conceive of biological treatments (i.e., gene therapy) for alcoholism targeted to inhibition of ALDH2. The major benefits to be gained lie in the greater specificity of such approaches (i.e., inhibition of only ALDH2, and possibly only hepatic ALDH2, as opposed to other enzymes) compared with the currently available drugs and the potential for longer action of the treatments. The specific aims of this proposal are: l. To determine the domains required for subunit interactions for the mitochondrial ALDH2 enzyme by binding studies and by use of the yeast two hybrid assay. 2. To determine the minimal sequence of the ALDH2*2 encoded subunit heeded to observe the dominant negative effect of this allele, using tissue culture models. This proposal does not address specific vectors or gene transfer technologies to be developed, since this is an area of intensive research being carried out by many other laboratories. The vectors thus developed will ultimately be available for use with any gene, and possibly for any tissue, of interest. Instead this proposal will lay the groundwork for the ultimate goal of control of the activity of ALDH2 in vivo. In the future, this could be tested for its ability to modify alcohol consumption.